This invention relates to electronic temperature controls and, more particularly, to electronic temperature controls for use with swimming pool and spa heaters.
Temperature controls employing mechanical control means have been used for many years to control the water temperature in swimming pool and spa heaters. A typical mechanical control employs a sealed temperature sensing metal bulb which is filled with a thermally expansive liquid. This bulb is connected to the actuating diaphragm of a pressure operated electrical switch through a metal capillary tube. The electrical switch in turn is connected to operate a heater controller such as an electric gas valve. In operation, the metal bulb is placed in close thermal contact with the water entering the heater. As the water temperature is increased by the heater, the fluid within the metal bulb expands in the capillary tube, exerting a pressure on the diaphragm of the electrical switch which is proportional to water temperature. The diaphragm in turn is biased against the capillary pressure by a spring. The spring force is adjusted by rotating a temperature control knob which serves as the temperature setting means. When the force of the expanding liquid exceeds the spring force, the diaphragm actuates the electrical switch which deenergizes the heater. Subsequent cooling of the water reduces the capillary pressure, thus deactivating the electrical switch, reenergizing the heater. Adjustment of the temperature control knob varies the spring force and thus sets the water temperature at which the heater will cycle on and off.
Although these and other types of temperature controls which employ mechanical control means have gained widespread use, they possess several limitations. For example, these controls possess a wide differential between the temperature at which the heater is turned on and the temperature at which the heater is turned off. This differential, or hysteresis, is largely caused by the backlash and the friction inherent in mechanically coupled systems. A wide differential in temperature results in user dissatisfaction because of the poor repeatability of temperature settings. This also results in energy waste since the user will typically increase the temperature setting in an effort to overcome the effect of the wide differential on the pool water temperature.
Another limitation of the prior art mechanical controls is their tendency to fail in a mode which results in an unsafe heater condition. A typical failure mode for these controls is a leak in the sensing bulb or capillary tube, with resultant loss of fluid pressure. This type of failure causes the heater to be energized continuously, which may damage the heater and may expose the user to dangerously high swimming pool and spa water temperatures. To overcome these problems, a separate high temperature sensor and safety switch is usually employed in prior art controls to deenergize the heater when water temperature rises above a preset maximum limit.
A further limitation of prior art controls is that they are not easily adapted for dual temperature control. Typically it is desirable for the user to be able to preset two different temperature settings for the heater, such as a high temperature mode for the spa, and a low temperature mode for the pool, with means for selecting the desired mode. With only a single temperature setting control, the user must adjust the control knob from one setting to the other to change modes. This results in poor temperature repeatability due to the wide control differential as described heretofore. Alternatively, two entirely separate controls may be employed, which requires duplicating the sensing bulbs, capillary tubes, diaphragms and pressure operated switches. A separate electrical switch is then employed to select the desired mode by connecting the appropriate pressure operated switch to the heater controller circuit. This duplication of control systems is expensive and cumbersome.
Still another limitation of prior art controls is that they are not easily adapted for use in remote control applications. In many instances it is desirable to control the heater temperature from locations other than the heater itself. For example, the heater may be located in an equipment area remote from the pool or spa, while the user may wish to control water temperature at a location adjacent to the swimming pool. The temperature sensing bulb in the prior art controls is typically mounted in the inlet water line of the heater, since this location closely approximates the spa or pool water temperature. Because the sensing bulb is connected to the temperature setting means by the metal capillary tube, the location of the setting means is restricted to the vicinity of the heater, precluding remote control.
It is therefore an object of the present invention to provide a new and improved temperature control for use in swimming pool and spa heaters.
It is another object of the present invention to provide a narrow differential temperature control for swimming pool heaters.
It is another object of the present invention to provide a swimming pool heater temperature control employing safety circuits to prevent injury to the user or to the heater in the event of a component failure.
It is another object of the present invention to provide a swimming pool heater temperature control easily adapted for use with multiple preset temperature settings.
It is still another object of the present invention to provide a swimming pool heater temperature control easily adapted for remote control of swimming pool and spa heaters.